Background: OA is a painful, disabling condition that disproportionately affects African Americans (AAs). Existing OA treatments yield only small to moderate improvements in pain and are not effective at reducing racial disparities in OA pain. According to the biopsychosocial model of pain, there is a need for novel pain interventions that target psychosocial factors associated with OA outcomes and disparities in OA outcomes. Evidence from the field of psychology suggests that an intervention designed to increase positive affect (PA), that is, feelings such as joy, excitement, or contentment, has the potential to improve pain and functioning and reduce racial disparities in patients with OA through multiple psychosocial mechanisms. PA interventions have been developed for clinical patient populations but have not yet been fully tested in patients with OA or in Veterans, nor have their effects on racial differences in clinical outcomes been examined. The proposed study will address these gaps by testing the impact of an evidence-based PA intervention on pain and functioning in AA and white Veterans with OA. Objectives: The primary aim of this study is to evaluate the impact of a PA intervention on pain and physical functioning in AA and white Veterans with knee/hip OA through a randomized, controlled, clinical trial. We hypothesize that patients randomized to a PA intervention will experience improved pain and functioning compared to patients randomized to an attention control (AC) program, and that these improvements will be larger for AAs than for whites. The secondary aim of this study is to identify variables that mediate the effects of the PA intervention on pain and functioning. We hypothesize that the effects of the PA intervention will be mediated by psychosocial variables known to be associated with OA outcomes or racial differences in OA outcomes (e.g., depression, self-efficacy, pain coping, perceived discrimination). Methods: A randomized, controlled, 2-arm design will be used to compare the effects of a 6-week PA intervention with that of an AC program on pain and functioning at 1, 3, and 6-months post-intervention among AA and white Veterans with knee/hip OA. Approximately 180 AA and 180 white primary care patients who meet clinical indications for knee or hip OA will be recruited from the Pittsburgh and Philadelphia VA Medical Centers. Eligible participants will complete an in-person baseline assessment of study outcomes, mediators, and control variables and be randomized to a 6-week PA or AC program. The PA program consists of completing 6 at-home activities (1 per week) that have been shown to increase PA. The AC program consists of 6 affectively neutral activities. Both groups will receive a weekly telephone call from trained interventionists to clarify instructions for the next week's activity and assess completion of the previous week's activity. Outcomes and proposed mediating variables will be assessed via telephone surveys at 1 month, 3 months, and 6 months post-intervention. Study outcomes include self-reported pain and physical functioning as measured by the Western Ontario MacMaster Index. Hypothesized mediators include depressive symptoms, positive/negative affect, satisfaction with life, arthritis self-efficacy, pain coping, pain catastrophizing, perceived discrimination, global stress, and social support. To assess intervention impact over time and by race (primary aim), we will fit linear mixed models that allow repeated measures on the continuous outcomes for each participant and assess change in outcomes over time. To identify mediators (secondary aim), we will use a multiple mediator bootstrap approach to assess whether the effect of the intervention is mediated by the hypothesized mediators.